The sternum or breastbone, in vertebrate anatomy, is a flat bone. It is shaped like a capital “T” located anteriorly to the heart in the centre of the thorax (chest). It connects the rib bones via cartilage, forming the anterior section of the rib cage with them, and thus helps to protect the lungs, heart, and major blood vessels from physical trauma. Its upper end supports the clavicles, and its margins articulate with the cartilages of the first seven pairs of ribs
A good number of surgical procedures on the thorax require median sternotomy. Median sternotomy provides a surgical approach to the heart and major arteries, lungs, mediastinum, and thoracic spine. The breast bone comprises a manibrium, superiorly, and a sternum, inferiorly.
Median sternotomy is a type of surgical procedure in which the sternum is cut longitudinally for entry into the thorax for exposure of heart and lungs during surgery. During surgery, the two halves of the bones are separated using retractors.
Following surgery, the sternum is approximated and held close together using various methods. Methods for re-approximation of sternum include using thin stainless steel wires, or stainless steel bands, or various sternal closure devices. Conventionally, thin stainless steel wires of about 1-1.5 mm diameter are used for closure of the sternum. Typically, a surgeon holds a needle using a strong needle holder and passes a wire around the left sternal half; either piercing the bone or going parasternal outside in. Then the wire is passed around the right sternal half inside out. The needle is cut and both the free ends of cut wires are held using clamps. After passing the required number of wires, haemostasis is checked. Then the wires are crossed individually and sternum is held closed together. The two ends of each wire are pulled across and twisted around each other so as to tighten the sternum. This procedure is repeated for all the wires. Excess wires are cut and the small twisted ends of wires are buried in the parasternal tissue to avoid cutting out of the sharp ends through skin. These wires remain permanently lodged and do not require removal unless any problem arises or unless there is a second surgical procedure.
Typically, tough stainless steel wires are widely used; but they have many disadvantages. Placement of wires often leads to bleeding from intercostals vessels during the passage of needle through parasternal tissue. Blood vessels can be punctured, leading to severe bleeding. Control of bleeding is time consuming and requires use of sutures, surgical clips, and electro cautery. This leads to increase in operating room time, exhaustion of surgical team, increase of cost of sutures and clips. Use of cautery often leads to weakening of wires and potentially decreases blood supply to the sternum leading to increased risk of sternal healing problems.
After haemostasis, during tightening of wires, some blood vessels may get injured leading to post-operative increasing drainage. This requires re-exploration and haemostasis. This again increases the cost of additional surgery, increases the risk of infection to patients. Also, additional blood and blood products are required for haemostasis and haemodynamical stability. It also results in increase of cost of antibiotics and blood and blood products, operating room time and increases strain on surgeons.
The sternum, following the surgery, has forces acting on it during breathing, coughing, and valsalva manoeuvre. This causes the sternum to retract away from each other causing stress on the stainless steel wire loops. The wires, being thin, can cut through bone leading to loosening of the sternal closure. This leads to sternal instability and risks of infection. This further leads to complete transaction of sternal bone and instability with infection called sternal dehiscence. This requires further surgical procedures, medications and antibiotics, prolonged hospital stay, and adds to the risk of mortality.
Such complications are occasionally seen in old patients or female patients with severe osteoporosis. The incidence of sternal dehiscence is also high among patients with Type II Diabetes mellitus.
Also, since the sternal wires occasionally break during tightening or during postoperative period leading to sternal instability, the broken loop often causes discomfort to the patients and protrudes out through the skin requiring second surgical procedure.
Wires and needles are sharp and can cause injury to the surgeon or the surgical team. Each cut end of wires is held in clamps and then there are several clamps in the surgical field. The cut ends often cut through the gloves and cause injuries to the surgeon/team. This accidental injury exposes the entire surgical team to blood borne diseases including AIDS, Hepatitis or the like infections or diseases or risks.
Further, the usage of stainless steel wires is often time consuming and adds on stress to the surgeon and the surgeon's team.
Other methods used for closure of sternum are sternal bands and sternal closure devices. Sternal bands are flat bands and avoid cut-through of sternums as seen in thin wires. However, bands are time consuming and difficult to apply and also the associated locking mechanism is often complex. Also during re-entry for emergency re-explorations, the bands are difficult to remove and can cause injury to underlying important organs including the heart.
Certain additional prior art clamping devices are also available for closure of sternum. Most of these devices have complex methods of applications and are also time consuming. They, however, overcome deficiencies of wire based sternal closures.